The present invention relates to a directional display, for instance for use as a three dimensional (3D) display. Such displays may be used in: professional displays, for instance in office environments; entertainment systems such as 3D video games; 3D television; medical imaging; virtual reality; and design visualization.
EP 0 656 555 discloses an observer tracking twin-panel display of the autostereoscopic 3D type. This display makes use of a beamcombiner to combine the outputs of two individual optical systems.
EP 0 726 482 and GB 2 297 876 disclose an autostereoscopic 3D display in which observer tracking is achieved by electronically changing the view information displayed by spatial light modulators. By changing the view information in response to movements of an observer, the observer can be tracked laterally while ensuring that the correct views are perceived by the individual eyes of the observer.
EP 0 721 131 and GB 2 296 617 disclose a similar type of observer tracking autostereoscopic 3D display but with the ability to track longitudinal movements of an observer. In this case, longitudinal observer movements are tracked by changing the view information in vertical slices of varying width.
For such lateral and longitudinal tracking displays, the viewing windows must be uniform and contiguous. Also, the width of the viewing windows is important. In a three-view system, the window width should be two thirds of the average inter-ocular separation whereas, in a four-view system, the window width should be half the inter-ocular separation. The appropriate viewing conditions for such displays may be achieved using spatial light modulators of the type disclosed in EP 0 625 861. However, such displays have various disadvantages. For instance, the image resolution is relatively low, in particular less that a third of the spatial resolution of the spatial light modulator for each image. Further, high manufacturing tolerances are required in order to avoid visible artifacts at the boundaries of viewing windows. Complicated interlacing of the images is required on the spatial light modulators. In order to provide a spatial light modulator of this type, a custom liquid crystal display (LCD) has to be manufactured or a conventional LCD panel, for instance of the delta type, has to be modified.
EP 0 947 208 and GB 2 320 156 disclose flat panel autostereoscopic 3D displays in which two parallax elements are used to improve the uniformity of viewing windows. One of the parallax elements defines the viewing windows but creates non-uniformities within the windows, for instance because of diffraction. The other parallax element introduces inverse illumination non-uniformities for canceling or reducing the undesirable optical effects of the first parallax element. The second parallax element does not modify the width or information content of the viewing windows and may be embodied as a gray-scale mask element. The embodiment shown in FIG. 30 of GB 2 320 156 discloses a directional illumination system in which a backlight and mask form a plurality of light sources which are imaged by a lenticular screen to form viewing windows.
It can be difficult for inexperienced observers of autostereoscopic 3D displays to position themselves correctly with respect to the viewing windows or viewing zones. EP 0 860 728 and GB 2 321 815 disclose a flat panel autostereoscopic 3D display which incorporates a visual position indicator integrated with a parallax element. This provides a relatively simple visual indication to the observer of correct and incorrect observer position with respect to the viewing zones or viewing windows.
EP 0 829 744, GB 2 317 295, EP 0 887 666 and GB 2 326 728 disclose parallax barriers which are suitable for use in directional displays and which permit different modes of operation to be achieved. Such a parallax barrier comprises polarization modifying strips for defining the slits of the parallax barrier separated by regions which do not affect the polarization of incident light. A separate removable uniform polarizer is provided. A further uniform polarizer is required and may be provided by an input or output polarizer of a spatial light modulator, such as an LCD. With the removable polarizer in place, a parallax barrier is formed to provide a 3D viewing mode. When the removable polarizer is removed from the optical path, the polarization modifying strips and the separating regions act as a uniformly transparent optical element for a 2 dimensional (2D) viewing mode.
Mashitani, xe2x80x9cAutostereoscopic LCD image splitter displaysxe2x80x9d, Optics Design number 12, pp 36-41 (the Optical Society of Japan, 1997) discloses a single-panel 3D display comprising an LCD with front and rear parallax barriers. The two parallax barriers cooperate to produce viewing zones having less overlapping edge regions than is produced by a single parallax barrier arrangement. This arrangement required non-directional illumination.
This arrangement narrowly constrains the profiles of the windows at the viewing plane so that the brightness of the displayed images is reduced and increased intensity variations are perceived as an observer moves by relatively short lateral distances with respect to the display. Also, the pitches of the parallax barriers are required to be substantially the same as the pixel pitch of the LCD. This requires high tolerance of alignment and manufacture and results in increased cost.
Nose et al, xe2x80x9cRear-lenticular 3D-LCD without eyeglassesxe2x80x9d, 3D Image Conference 1997, pp219-224 discloses a 3D display in which a horizontal parallax system and a vertical parallax system cooperate to allow autostereoscopic 3D viewing from a single LCD panel in viewing zones restricted horizontally with the images interlaced in adjacent rows of picture elements (pixels) on the LCD. This arrangement simplifies the interface to the LCD by permitting two images to be displayed as the interlaced fields of the standard interlaced video format. The horizontal parallax system defines both the information content of viewing regions and, in combination with the vertical parallax system, the form of the viewing regions. Directional illumination is required and is effectively split into two sub-systems, with light from each sub-system passing through parts of the display to define the information content of the viewing zones. Thus, the directional illumination is effectively divided into two spatially multiplexed systems, each of which is only associated with some of the pixels of the LCD.
This arrangement also suffers from the disadvantage of requiring alignment of the optical elements substantially at the pixel pitch of the LCD. Further, a lenticular screen is required with the pitch of the lenticules being substantially equal to the LCD pixel pitch. Lenticular screens are difficult and expensive to manufacture with the tolerances required to achieve accurate alignment with LCD structures, particularly when compared with parallax barriers which may be made to high tolerances using standard photographic or lithographic techniques.
GB 2 252 175 discloses a single panel autostereoscopic 3D display using a double parallax barrier arrangement. This arrangement comprises two separate barrier sheets working together to define broad illumination regions with non-illuminated regions separating them. In this way, pseudoscopic viewing zones can be avoided. However, such an arrangement also suffers from spreading of the edges of the window profile illumination resulting in perceptible variations in image brightness as an observer moves laterally. Also, such an arrangement cannot provide a 2D viewing mode.
GB 2 317 710 discloses a directional display in which a lenticular screen is associated with an active mask arrangement forming a rear parallax barrier. The combination may be considered to act as a directional light source which illuminates an associated spatial light modulator. However, no parallax optic is associated with the spatial light modulator.
GB 2 272 555 discloses what is known as a xe2x80x9chybrid sandwichxe2x80x9d type of stereoscopic display. The hybrid sandwich comprises a spatial light modulator having input and output parallax optics. The input parallax optic effectively images the light sources at a diffuser within the sandwich and so does not act as a directional illumination system.
EP 0 570 179 discloses a similar arrangement in which a hybrid sandwich is associated with a directional light source. However, the directional light source merely serves to alter the direction of input illumination to the hybrid sandwich.
According to the invention, there is provided a directional display including a spatial light modulator, a directional illumination system for directing light through the modulator, and a parallax optic associated with the modulator, wherein: the illumination system directs light towards a plurality of first notional viewing windows, each of which has a first lateral extent; the parallax optic cooperates with the modulator so that non-directional illumination of the modulator would result in the formation of second notional viewing windows, each of which has a second lateral extent; and the modulator, the illumination system and the parallax optic cooperate to form actual viewing windows, each of which has a lateral extent which is equal to the product of the first and second lateral extents and is less than each of the first and second lateral extents.
The term xe2x80x9clateral extent of a viewing windowxe2x80x9d means the lateral width for which the light intensity (for a maximally white image) is greater than x % of the peak intensity of the window, where x is less than 100. In theory, x can have any value less than 100 but, in practice, values of x which are so low as to be affected by stray light, crosstalk, etc. should be avoided.
The illumination system may include at least one illumination source and an imaging system.
The illumination system may include a plurality of discrete light sources.
The imaging system may include a field lens.
The illumination system may include a backlight and a mask having a plurality of slits defining the illumination sources. Regions of the mask between the slits may be reflective towards the backlight. The imaging system may comprise a lenticular screen. Each lenticule of the lenticular screen may cooperate with a group of the slits to image the slits in a plurality of lobes in respective viewing windows.
The imaging system may include at least one holographic optical element. The illumination source may comprise a collimated light source.
The viewing windows may be laterally contiguous.
The viewing windows may include laterally spaced pairs of laterally contiguous viewing windows.
The parallax optic may include a parallax barrier.
The spatial light modulator may include a first and second spatial light modulators, the parallax optic may include first and second parallax optics cooperating with the first and second spatial light modulators, respectively, and the display may include a beamcombiner for combing out put light from the first and second spatial light modulators. The illumination system may include a plurality of discrete light sources and a beam splitter for directing light from the light sources towards the first and second spatial light modulators.
The display may include a switchable diffuser cooperating with the spatial light modulator and switchable between a non-diffusing state to provide a directional display mode and a diffusing state to provide a non-directional display mode.
It is thus possible to provide a directional display in which directional illumination creates illumination zones with light passing through the whole area of a directional display panel. The directional display panel defines the image information content visible in the whole or part of the illumination zones. By using imaging optical elements to provide the directional illumination, improved illumination zone profiles can be achieved such that uniform illumination is provided in a central part of the illumination zone and the zone has sharp edges. The use of a parallax optic such as a parallax barrier to define the information content of the zones provides low levels of crosstalk.
It is further possible to provide an electronically tracked autostereoscopic 3D display of the beamcombiner type. Such an arrangement requires no moving parts and results in little or no visual flicker artifacts during observer tracking. A four-window system can be provided for enhanced tolerances during tracking, for instance compared with a three-view system as disclosed in EP 0 726 482, EP 0 721 131, GB 2 297 876 and GB 2 296 617. Longitudinal tracking by means of view slicing can be provided and fast observer tracking at video input rates can be achieved. An image resolution equal to half the spatial resolution of the spatial light modulator can be provided. The spatial light modulator may be embodied by standard liquid crystal displays without requiring any modification. Such an arrangement can make use of the same display interfacing as other flat panel two-view interlaced displays. In the case of a parallax barrier as the parallax optic, wide slits may be adopted so as to improve light efficiency and reduce diffraction effects. All of the elements may be fixed in position during manufacture so as to provide a rugged display. Stereoscopic and 2D modes of operation may easily be provided in some embodiments.
It is possible to eliminate pseudoscopic viewing regions, for instance for fixed observer position to two-view autostereoscopic displays. Such arrangements can have reduced crosstalk and may be electronically switchable to a 2D mode. Further, it is not necessary to provide any viewer position indication because even inexperienced observers have no substantial difficulty in correctly locating themselves with respect to the viewing regions.